Does the Cx51 compiler support I2C operations such as addressing external RAM for XDATA fetches? Or, do you still have to have the standard RAM (address lines) if you require excess XDATA space (more than 2K in the case of the 89C669)?
one issue: If you willy-nilly use serial RAM as XDATA your process speed will comre to a crawl. I guess the reason for your question is the old issue "I need more port pins" A much better alternative is to use parallel RAM and memory map some I/O. -OR- if you do not need more than 64k of code space, switch to the 668 which has 8k of internal RAM even more dramatic use a SILabs F12x, you get 8 ports, 128k of internal code memory and 8k of internal RAM. Erik